The technique also reduced the cost of tests for contaminants due to its improved sensitivity and selectivity—using only half the materials needed with the previously used techniques and analyzing them at a lower concentration. The ability to eliminate the matrix effect also reduced the need for time-consuming purification steps, helping IQSTAP to provide faster results for time-sensitive analyses.
Overcoming the Limitations of Electron Ionization
Traditionally, electron ionization (EI) based systems have been used for the determination of dioxins and other persistent organic pollutants, this technique however, produces significant amounts of fragment ions. But some of the compounds of interest for IQSTAP scientists were not suitable for ‘hard’ ionization analysis, such as EI. One of the key limitations to this technique is selectivity, as it gives rise to identical ions for different compounds. This technique can make it challenging to see the whole molecule, for example, it can result in the same fragment for compounds with different numbers of bromine atoms.
However, APGC results in a “soft” ionization process where the molecule is ionized by either proton transfer or charge transfer, rather than by direct electron bombardment. This soft ionization with APGC was extremely beneficial for the IQSTAP team’s work because of the reduced fragmentation for many compounds. This can result in higher sensitivity and specificity, therefore simplifying precursor ion selection in MS/MS analyses. The APGC soft ionization method is suitable for the analysis of many easily degradable compounds. That’s particularly helpful with dioxin analysis, where EI has significant limitations.
The IQSTAP scientists also found the analysis of samples by APGC allows for improved selectivity when generating multiple reaction monitoring transitions in comparison to the significant fragmentation experienced with EI gas chromatography. Operating the GC system at atmospheric pressure provides increased scope for ionization mode optimization—namely charge and proton transfer.
The technique has ability to have both GC and LC coupled to the same mass spectrometer, and has a relatively quick and simple changeover from LC to GC and vice versa—which is important since many analyses cross the boundary between LC and GC.
Shaping the Future of Food Safety
Continuous changes in research into dioxins drive the need for ever-lower limits of detection and quantification. APGC has proved to provide the speed, selectivity, and sensitivity needed for dioxin analysis. Researchers at IQSTAP concluded that their results with APGC are encouraging for food safety, and plan to continue to improve the analysis of other persistent organic pollutants using APGC and subsequent compliance in dioxin analysis.
Dr. Li is an assistant professor IQSTAP. Reach her at firstname.lastname@example.org.